1. INTRODUCTION Study of the Pannonian sediments in the southwest- ern part of the Medvednica Mts. (Fig. 1) and their rela- tionship with underlying Sarmatian deposits, revealed two entirely new forms of the genus C o n g e r i a . GOR- JANOVI∆-KRAMBERGER (1890) noticed and briefly described a new congerian form from the “Praepontian white marls” from the VrapËe locality, but he did not establish and name a new species, because of the small number of specimens and their poor preservation. Dur- ing this study, a collection of approximately 20 speci- mens of this form has enabled the establishment of a new species, Congeria baschi n.sp., which can be clea- rly identified and positioned in a stratigraphically nar- row interval. The presumption has been made, that C . b a s c h i n.sp. represents the ancestral form of the forth- coming radiation of congerian species (see Fig. 10). SREMAC (1981) described C. vugroveci as a new species from the Upper Pannonian marls of Vugrovec in the southeastern part of the Medvednica Mts. (North- New Congerian Species and Their Similarity with Congeria banatica from the Pannonian Sediments in Northern Croatia Davor VRSALJKO 1 and Jasenka SREMAC 2 ern Croatia), distinguishing it from the previously kno- wn C. banatica HÖRNES. Several specimens have been collected during this study, thus confirming the validity of C. vugroveci. Previous authors dealing with C. bana - t i c a (HÖRNES, 1875; KOCHANSKY-DEVIDÉ, 1976; SREMAC, 1981; VRSALJKO, 1997) noticed the vari- ability of this form and its separation into three main morphological varieties. In this study, we will discuss this variability and use the biometrical statistics (see Fig. 8) to describe one of these forms as the entirely new species, Congeria susedana n.sp. ANDRUSOV (1964) described congerian taxa belonging to the group S u b g l o b o s a e as “indicative of calm and sheltered, oligohaline lacustrine palaeoenvi- ronments”, stratigraphically positioned within the Pan- nonian stage. According to the morphology of the shell, the new species described in this paper could belong to the Subglobosae. The term “group”, although not found in the ICZN (International Codex of Zoological Nomen- clature), has been applied to congerian bivalves by many authors since ANDRUSOV (1964), in order to express the typical morphotypes. There have been sev- eral attempts to equate congerian “groups” with legal taxonomical categories (e.g. genus, subgenus), but the collected fossil material is rarely preserved well enough to enable this task. Populations of Congeria baschi n.sp. can commonly be found in the Lower Pannonian limestones and marls (Fig. 3) which were deposited in an almost freshwater (VRSALJKO, 1997), shallow lacustrine palaeoenviron- ment. From the same horizon, a rich molluscan commu- nity has been collected including: Radix (Radix) croati - ca (GORJANOVI∆), R. (R. ) extensa ( G O R J A N O V I ∆ ) , Gyraulus (G y r a u l u s) p r a e p o n t i c u s ( G O R J A N O V I ∆ ) , Orygoceras laevis GORJANOVI∆, Limnocardium pra - eponticum ( G O R J A N O V I ∆ ), L. spinosum ( L Ö R E N- THEY). L. plicataeformis (GORJANOVI∆) and others. An associated ostracod assemblage from the same hori- zons contains Hungarocypris auriculata ( R E U S S ) , A m - plocypris abscisa (REUSS), Candona (Pontoniella) croatica S O K A » , C. (T h a m i n o c y p r i s) hodonensis P O- KORNY and others. In the uppermost sections of the Upper Pannonian marls, rare specimens of Congeria susedana n.sp. have been found (Fig. 4). These marls were deposited in the relatively deep, distal parts of the lake (VRSALJKO, G EOL. C ROAT. 52/2 99 - 108 10 Figs. 1 Pl. ZAGREB 1999 Key words: Pannonian Lake, Miocene, Pannonian Basin, NW Croatia, Congeria , Bivalvia, New speci- es, Endemic evolution. 1 Institute of Geology, Sachsova 2, HR-10000 Zagreb, Croatia. 2 Department of Geology and Palaeontology, Faculty of Science, University of Zagreb, Ul. kralja Zvonimira 8, HR-10000 Zagreb, Croatia. Abstract Congeria baschi n.sp. and Congeria susedana n.sp. are two new species from the Pannonian sediments of the Medvednica Mts. (NW Croatia). C. baschi n. s p . was found in the Lower Pannonian lime- stones, and C. susedana n.s p . was collected from the Upper Pannon- ian marls. Relationships with the affiliated taxa enable reconstruction of a phyletic lineage beginning with Congeria soceni JEKELIUS, through C. baschi n.sp. to Congeria banatica HÖRNES. C. banatica is the ancestor of two branches, leading to C. susedana n. sp. and C. vugro - veci SREMAC, respectively. Dreissenomya digitifera (ANDRUSOV) is the probable descendant of C. vugroveci. The accompanying assemblages of fossil molluscs and ostracods from the same horizons facilitate the precise stratigraphic and palaeoenvironmental positioning of the new taxa. 100 Geologia Croatica 52/2 1997). Among the accompanying molluscs, the most important taxa are: Gyraulus (G. ) tenuistriatus ( G O R- JANOVI∆), Limnocardium winkleri ( H A L A V A T S ) , Paradacna syrmiense (HÖRNES), ?Cerastoderma mar - garitacea (BRUSINA), and ?C. protracta (GORJANO- VI∆). Among the numerous ostracods, the following taxa are extremely abundant: Hungarocypris hierogly - phica (MEHES), Amplocypris dorsobrevis S O K A » , Cypria dorsoconcava KRSTI∆, Candona (P o n t o n i e l l a ) sagittosa KRSTI∆ and C. (L i n e o c y p r i s) pupini K R S- TI∆. 2. MATERIAL AND METHODS Numerous specimens of D r e i s s e n i d a e mussels were collected during facies research of Neogene sediments of Mt. Medvednica (NW Croatia). Several Pannonian localities were investigated, including VrapËe and Pod- sused in SW Medvednica Mt., where detailed strati- graphical columns were reconstructed (Figs. 1, 3 and 4). Previously collected Pannonian congerian speci- mens from the Croatian Museum of Natural History (GORJANOVI∆, 1890) and Faculty of Science in Zag- reb (SREMAC, 1981), as well as the sketches published by HÖRNES (1875) were taken into consideration. Shells of the available fossils were measured with calipers (20 specimens of C. banatica , 17 specimens of C. baschi n.sp., 6 specimens of C. susedana n.sp. and 5 specimens of C. vugroveci). Specimens published by HÖRNES were measured from sketches. Angles were also measured from shells or from sketches, but only on completely preserved specimens. The shell material is, unfortunatelly, poorly preser- ved. Impressions and moulds are more common than Fig. 1 Location map: a) Podsused; b) Bol- fani; c) VrapËe; d) Medvedski Breg; e) Vugrovec; f) Goranec; g) MoravËe; h) KoroviÊ; i) Banovina region. Fig. 2 Schematic sketch of the morphometric shell elements in the genus C o n g e r i a : h) height; l) length; c) convexity; dl) length of the dorsal edge; k (h/l) elongation rate; α) angle between the ven- tral and the dorsal edge; β) angle between the dorsal and the anal edge; γ) angle between the dorsal edge and the border of the pseudolunular field; 1) beak; 2) main ridge; 3) ventral field; 4) dorsal field; 5) wing shaped extension; 6) mould of the ligament lamella; 7) pseudolunular field; 8) secondary ridge; 9) growth lines. complete shells. Therefore most of the conclusions were based on the external shell morphology. A disperse diagram for C. banatica and C. susedana n.sp. considering height/length ratio versus the length of the dorsal edge was prepared. Biometry in this case was just an auxiliary method, because the number of specimens (except for C. banatica ) was too small for the relevant statistical conclusions to be drawn. 3. TAXONOMY Class BIVALVIA Subclass Heterodonta NEUMAYR 1884 Order Veneroida ADAMS & ADAMS 1856 Family Dreisseniidae GRAY & TURTON 1840 Genus Congeria PARTSCH 1835 (Group Subglobosae ANDRUSOV 1897) Congeria baschi n.sp. (Pl. I, Fig. 1) 1890. Congeria sp. GORJANOVI∆-KRAMBERGER; GORJANOVI∆-KRAMBERGER, p. 163, pl. 6, fig. 21. 1964. Congeria sp. GORJANOVI∆-KRAMBERGER; ANDRUSOV, p. 425, pl. 1, fig. 20. 101Vrsaljko & Sremac: New Congerian Species and Their Similarity with Congeria banatica ... Fig. 3 VrapËe - type local- ity of Congeria baschi n. sp. Lithological col- umn (For legend see Fig. 10): 2) sand; 3) marl; 4) clay; 5) lime- stone. 1997. Congeria sp. GORJANOVI∆-KRAMBERGER; VRSALJKO, p. 40, type 8. Holotype (Fig. 5 - 1*) is stored in the Department of Geology and Palaeontology of the Croatian Museum of Natural History in Zagreb (Inventory No. 290). It was found at VrapËe locality, in the southwestern part of Medvednica Mts., and was presented by GORJANO- VI∆-KRAMBERGER (1890; p. 163, pl. 6, fig. 21). GORJANOVI∆-KRAMBERGER (1890) was the first to find two specimens in the “Praepontian” (= Lower Pannonian) marls from the surroundings of VrapËe village in the Medvednica Mts. He determined them as belonging to the genus C o n g e r i a , offering a short description of the smaller specimen: “Specimen is 8.5 mm long, and 5 mm wide, triangular in outline. Posterior edge is slightly extended, ridge is blunt, and the beak is weakly pointed out and incurved”. The same author furthermore claimed that, due to the small num- ber of specimens and their poor preservation, which made the reconstruction of the shell impossible, he could not offer a more detailed description, and deter- mined this form to be only Congeria sp. After collecting twenty new specimens, we can con- clude that this small congerian taxon always appears within the Radix croatica Zone. Due to its morphologi- cal features it deserves to be described in detail, and acquire the status of a new species. 102 Geologia Croatica 52/2 Derivatio nominis: The species is dedicated to the well known Croatian palaeontologist Oto Basch, employed in the Institute of Geology in Zagreb, who, with his encyclopedic knowledge, strongly influences the education of young geologists, and makes signifi- cant contributions to Croatian geology with his pub- lished papers. Locus typicus: Specimens No. 1 and 2 have been collected near VrapËe village in the western part of the Medvednica Mts., at the same locality which was first studied by GorjanoviÊ-Kramberger (holotype 1*), and consists of thin-bedded limestones (ca. 20 cm), inmedi- ately above the Sarmatian/Pannonian boundary (Fig. 3). Most of the other specimens have been also found in the vicinity of VrapËe village, and several of them were collected in the Banovina district. Stratum typicum: Lower Pannonian, Radix croati - ca Zone. Diagnosis: Very small, in most cases triangular, significantly convex shell. Outer shell surface with pri- mary ridge close to the anterior field, and extremely weak secondary ridge close to the posterior field. Poste- rior field with weakly pronounced wing-shaped exten- sion. Description: Small-sized, rather convex shell, trian- gular in outline, with clearly developed growth lines and indistinct wing-shaped extension on the posterior Fig. 5 Specimens of Congeria baschi n.sp. from the VrapËe locality: 15) adult form; 1) juve- nile specimen; 1*) holotype from GOR- JANOVI∆-KRAMBERGER (1890).15 1 1* Fig. 4 Podsused - type locality of C o n g e - ria susedana n. sp. Lithological col- umn: 1) gravel; 3) marl; 4) clay; 5) limestone. 103Vrsaljko & Sremac: New Congerian Species and Their Similarity with Congeria banatica ... field, which becomes well developed in older speci- mens. No specimen with preserved shell material has been found. Imprint of the ligament lamella, extending along the dorsal edge, almost half of its length, can often be observed. Umbo small, sharp, slightly incurved forward. The median, most convex part of the shell, bears two ridges. Main (primary) ridge is well devel- oped, situated closer to the anterior field, straight to slightly incurved, and rounded in cross section. Sec- ondary ridge is situated at the posterior field, it is more rounded, and is particularly well-developed in younger specimens. Elongation rate (k), defined in Fig. 2, is almost constantly 1.5. The sum of the angles between the dorsal edge and the edge of the anterior field (α) and the angle between the dorsal edge and the edge of the posterior field (β) is almost always 180° (see Fig. 2). In adult shells, due to the weak winglike extension, this angle decreases in value by ca. 10 degrees. Dimensions: Spec. h l dl c α β k Locality (mm) (mm) (mm) (mm) (°) (°) 1* 8.5 5.0 4.0 2 60 120 1.7 VrapËe 1 3.0 2.0 1.5 1 50 130 1.5 VrapËe 2 3.0 2.0 1.5 1 50 130 1.5 VrapËe 3 3.0 2.0 - - - - 1.5 Bolfani 4 7.0 4.5 - - - - 1.5 Banovina 5 9.0 5.5 5.0 2 60 120 1.6 Bolfani 6 5.0 3.0 - - - - 1.6 Banovina 7 5.0 3.0 - - - - 1.6 VrapËe 8 7.0 4.5 - - - - 1.5 VrapËe 9 8.0 5.0 - - - - 1.6 VrapËe 10 8.0 5.0 - - - - 1.6 VrapËe 11 6.5 4.0 - - - - 1.6 VrapËe 12 9.0 5.5 - - - - 1.6 VrapËe 13 4.0 2.5 - - - - 1.6 VrapËe 14 8.0 5.0 - - - - 1.6 VrapËe 15 7.5 4.5 4 2 60 120 1.5 VrapËe 16 12.0 7.5 - - - - 1.6 Banovina 17 4.5 3.0 - - - - 1.5 Banovina Comparison: Congeria baschi n. sp. strongly res- embles C. neumayri ANDRUSOV (ranging from the “Helvetian” to the Pliocene) in its shape, and the posi- tion of the main ridge. ANDRUSOV (1964) reports the presence of typical specimens from the marine Miocene at the Laa locality (of Karpatian age), and PAPP (1954) considers C. neumayri to be persistent in a wide salinity range. According to its main features, C. baschi strong- ly resembles C. jadrovi BRUSINA, from the Lower Pliocene freshwater sediments of Sinjsko polje, altho- ugh. ANDRUSOV (1964) related C. neumayri and C . j a d r o v i with the group M y t i l i f o r m e s, thus making a comparison with C. baschi n.sp. barely possible. It is more probable to presume the origin of C. baschi f r o m similar older Sarmatian taxa, such as C. soceni J E K E- LIUS and/or C. moesia JEKELIUS, scarce brackish representatives of the group Subglobosae. PAPP (1954) collected and described these taxa from the Sarmatian and the Pannonian (Zones A and B) of the Vienna basin. Congeria banatica HÖRNES (Pl. 1, Fig. 2) 1 8 7 5 . Congeria banatica nov.sp.; HÖRNES, p. 75, pl. 3, figs. 3-5. 1 9 6 4 . Congeria banatica HÖRNES; ANDRUSOV, p. 132-133, pl. 11, figs. 18-20. 1990. Congeria banatica HÖRNES; VRSALJKO, p. 38, type 1. Short description: Adult form - Type A(HÖRNES, 1875; pl. 3, fig. 3) Small-sized shell, rather convex, elongate-trape- zoidal in outline. Shell material usually not preserved. Well exposed, dense growth lines; impression of the ligament lamella following the dorsal edge, almost half of its length. Posterior field with small wing-shaped extension. Ridge well-defined, sharp in the umbonal portion, becoming string-like in adult specimens, slight- ly rounded, slightly incurved towards the anterior field. Umbo small, weak, incurved forward. Juvenile form - Type B(HÖRNES, 1875; pl. 3, fig. 2) Shell smaller and less convex than in the A-type. Numerous, weaker growth lines. Trapezoidal outline, without the winglike extension. Ridge well defined, sharp, string-like, rounded only in the youngest portion of the shell, incurved as the elongate “S” and dislocated towards the anterior portion. Umbo weak, sharper than in A-type, and incurved forwards. Adult form - Type C(VRSALJKO, 1997; p. 38, type 1) Similar to type A, but shell more elongate and more convex. Elongate-trapezoidal in outline. Ridge situated almost in the middle of the outer shell. Common features: Younger specimens possess well-developed and sharp ridge, while the adult shells bear string-like ridges and wing shaped extensions at the posterior field. Dimensions: Spec. h l dl c α β k Locality (mm) (mm) (mm) (mm) (°) (°) From HÖRNES (1875) Type A 17 16 13 ? 70 110 1.0 Banat Type B 13 9 9 ? 70 120 1.4 Banat This study 1 16 13 13 2.0 70 100 1.1 Medv.Breg 2 18 12 10 3.0 80 130 1.5 MoravËe 3 21 18 14 2.0 70 110 1.1 KoroviÊ 4 19 14 12 3.0 80 120 1.2 Podsused 5 20 15 12 3.0 80 120 1.3 Podsused 6 18 15 12 3.0 90 120 1.2 Podsused 7 18 13 12 3.0 80 110 1.3 Podsused 8 14 10 8 1.5 80 120 1.4 Podsused 104 Geologia Croatica 52/2 9 15 10 9 1.5 70 120 1.5 Podsused 10 12 9 8 2.0 70 120 1.3 Podsused 11 15 10 9 3.0 80 120 1.5 Goranec 12 16 11 9 2.5 90 120 1.4 Goranec 13 17 12 8 2.5 70 110 1.4 Vugrovec 14 15 11 8 2.0 80 110 1.3 Vugrovec 15 22 18 12 3.0 70 130 1.2 Banovina 16 21 18 12 2.5 70 130 1.1 Banovina 17 18 15 12 3.0 90 130 1.2 Banovina 18 20 16 13 3.0 80 110 1.2 Banovina 19 21 17 13 2.5 70 110 1.2 Banovina 20 22 19 14 3.0 70 100 1.1 Banovina Congeria susedana n.sp. (Pl. 1, Fig. 4) 1997. Congeria aff. banatica HÖRNES; VRSALJKO, p. 38, type 2. Derivatio nominis: Species has been named after the famous historic fortress Susedgrad, near which the abandoned quarry of cement marls with most of the described specimens is located. Holotypus: Specimen No. 1. Locus typicus: Podsused, western part of Zagreb, widely exposed profile of marly sediments near the for- mer cement factory (Fig. 4). Stratum typicum: Upper Pannonian; uppermost part of deepwater lacustrine marls, in the C o n g e r i a banatica Zone. D i a g n o s i s : Very small, rather convex shell, trape- zoidal in outline, with wide dorsal field and distinct wing shaped extension. Description: Small-sized shell, prominently con- vex, trapezoidal in outline, with distinct, closely-spaced growth lines and well-developed wing shaped extension at posterior field. In most cases a thin calcite shell layer is preserved. Cast of the ligament lamella along the dor- sal edge is well developed and extends over half its length. Umbo small, sharp and weakly incurved for- ward. Almost in the middle of the outer shell, a distinct ridge can be observed, rather sharp near the umbo, and weakly rounded and arcuate forward at the front. Adult specimens are slightly more elongate. Dimensions: Spec. h l dl c α β k Locality (mm) (mm) (mm) (mm) (°) (°) 1 11 12 10 2 80 120 0.9 Podsused 2 9 10 7 2 80 120 0.9 Podsused 3 10 11 8 3 80 120 0.9 Podsused 4 11 10 7 3 80 120 1.1 Podsused 5 12 11 8 2 80 120 1.1 Medv.Breg 6 12 11 8 2 80 120 1.1 Medv.Breg C o m p a r i s o n : Congeria susedana n. sp. strongly resembles C. banatica HÖRNES in shape and ridge position, but the difference appears in the decreased size of the shell, arcuate ridge and longer mould of the ligament lamella. According to its appearance in similar facies and somewhat younger horizons, a narrow link of the new species with C. banatica is proposed (see Fig. 10). Some similarities in size and outline with C. vugro - veci SREMAC can be observed, but the latter is charac- terised by the appearance of the pseudolunular field. Many previous authors considered C. susedana t o be a variety of C. banatica , but, according to the prono- unced biometric difference this form deserves to be established as a new palaeontological species. Congeria vugroveci SREMAC 1981. Congeria vugroveci n.sp.; SREMAC, p. 109, pl. 1, figs. 1-4. Fig. 6 Specimens of C. banatica HÖRNES (HÖRNES, 1875): Type A - adult specimen, from the Banat district and Type B - juvenile form, from the Banat district; 7) adult specimen from Podsused. Type A Type B 7 105Vrsaljko & Sremac: New Congerian Species and Their Similarity with Congeria banatica ... Short description: Shell small-sized, rather inflat- ed, trapezoidal in outline, with distinct, closely spaced growth lines. Mould of the ligament lamella can often be observed along the entire dorsal edge. Imprint of the posterior lamella extends almost half the length of the dorsal edge, and the anterior mould is weakly devel- oped and very short. At the anterior side a weak ridge can be observed, thus producing a small pseudolunular field. Ridge is distinct, sharp and very slightly incurved in shape of the elongate “S” form, dividing the outer shell surface into two almost equal portions. Umbo is weak, rather wide, blunt, and very slightly incurved toward the anterior portion of the shell. Dimensions: Spec. h l dl c α β γ k Locality (mm) (mm) (mm) (mm) (°) (°) (°) 1 6.5 6 5 1.0 60 100 120 1.0 Med.Breg 2 8.0 6 - - - - - 1.2 Med.Breg 3 7.0 5 - - - - - 1.2 Med.Breg 4 14 13 12 2.0 70 110 110 1.0 Goranec Holotype 1* 8 9 8 1.5 75 105 130 0.9 Vugrovec According to the development of the anterior mar- gin and the appearance of the pseudolunular field, this form can be closely related to the genus D r e i s s e n o m y a (FUCHS, 1870 - from BASCH & ÆAGAR-SAKA», 1992). Considering the similarity and its appearance in older sediments (Upper Pannonian), C. vugroveci could be the possible ancestral form for some younger Pon- tian species, such as Dreissenomya digitifera A N D R U- SOV. 4. DISCUSSION AND CONCLUSIONS In this paper two new species of congerians from the Pannonian marls from northern Croatia, C o n g e r i a baschi n. sp. and C. susedana n. sp. are described and figured (Figs. 5 and 7; Pl. I, Figs. 1, 3, 4 and 5). For Congeria vugroveci SREMAC (Fig. 9) a partial revi- sion and completion of the description has been made. Reconsidering the variability of C. banatica H Ö R- NES, as noticed by most of the previous authors, a reconstruction of the types of HÖRNES (1875; Pl. 3, Figs. 2 and 3) is offered and compared with our speci- mens (Fig. 6; Pl. I, Figs. 2 and 6). We have found that C. banatica is a variable form, but C. susedana n. s p . described here can hardly be considered just a variety of C. banatica due to the completely different morpho- metrical features of the shell. According to the rather short stratigraphic range of C. banatica , as well as its constant palaeoenvironmental characteristics, it is hard to envisage considerable variability. Studying the 20 specimens of C. banatica collected during our research a common feature can be observed. The ridge of the younger specimens is sharper and distinct, while in adult shells it becomes rounded, and the posterior field extends into a wing-shaped form. The elongation rate in adult shells is decreasing. Fig. 8 Scatter plot showing the relationship between the elongation rate (k) and the length of the dor- sal edge (dl). Fig. 7 Specimen of the Congeria susedana n.sp.; reconstruction of the holotype. 106 Geologia Croatica 52/2 Special attention has been paid to the C. banatica HÖRNES, and its relationship with C. vugroveci S R E- MAC and C. susedana n.sp. These two species are the possible descendents of C. banatica . For the Early Pan- nonian C. baschi n.sp. there are indications that it origi- nates from some similar Sarmatian brackish forms, introduced by PAPP (1954). This small species from the lowermost Pannonian beds is almost the unique rep- resentative of C o n g e r i a (in lacustrine sediments) and, knowing that most congerian species appear first in the Late Pannonian substage, it could be considered one of the possible ancestral forms for the later explosion and divergence of the species (Fig. 10). The main ecological factor influencing the variabili- ty of brackish and freshwater faunas, including congeri- ans, is geographical isolation and decrease of salinity. The diversification of congerian taxa into the groups (sensu ANDRUSOV, 1964) obviously needs critical revision based on morphological features and new palaeoenvironmental data (I. MAGYAR, personal com- munication). Such revision would provide better foun- dation for the reconstruction of phylogenetic relation- ships within the family Dreissenidae . Studying the associated assemblage of fossil mol- luscs and ostracods from the same horizons, newly established congerian forms can be placed in the previ- PLATE I 1 and 3 Congeria baschi n.sp., Early Pannonian, from the VrapËe locality; 1) x10, 3) x2. 2 and 6 Congeria banatica HÖRNES, Late Pannonian, from the Podsused locality; 2) x6, 6) x4. 4 and 5 Congeria susedana n.sp., Late Pannonian, from the Podsused locality; 4) x6, 5) x4. Fig. 9 Specimens of Congeria vugroveci SREMAC: 1) juvenile form from Medvedski Breg; 1*) adult specimen, reconstruction of the holotype. 1 1* Fig. 10 Stratigraphic range and the sug- gested relation- ship among the congerian species. 107Vrsaljko & Sremac PLATE I 108 Geologia Croatica 52/2 ously defined biostratigraphic zones for the Pannonian stage. So Congeria baschi n.sp. belongs to the B (?AB) Zone according to PAPP (1953), or β ( ?α) - phase (according to SOKA», 1972), and C. susedana n. s p . the D Zone or ?δ - phase. Acknowledgements Most of the fossil molluscs were collected during the year 1993, within the project “Facies and physical features of the Neogene carbonate sediments”, when, at the suggestion of the project manager M. PIKIJA the idea for this research was born. We thank K. ©IKI∆ for the fossil material from the wider area of Banovina. Determination of ostracods has been performed by Mrs. Valentina HAJEK-TADESSE. We express our grati- tude to Mrs. Zlata JURI©I∆-POL©AK from the Croat- ian Museum of Natural History who allowed us to reconsider the type congerian specimens from the Gor- janoviÊ collection. 5. REFERENCES ANDRUSOV, N. (1964): Fossil and living D r e i s s e n i - dae from Europe and Asia.- Izbrannije trudi, 3, Col- lected works (reprint edition), 1-404, Moskva. BASCH, O. & ÆAGAR-SAKA», A. (1992): Pontian Dreissenidae (M o l l u s c a, L a m e l l i b r a n c h i a t a ) f r o m Croatia.- Acta geologica, 22/1, 31-60, Zagreb. GORJANOVI∆-KRAMBERGER, D. (1890): Die Fau- na der praepontischen Bildungen von VrabËe.- Gla- snik hrv. narav. druπtva, 5, 154-163, Zagreb. HÖRNES, R. (1875): Tertiär-Studien (VI).- Jahrbuch Geol. Reichsanst., 25/1, 63-87, Wien. KOCHANSKY-DEVIDÉ, V. (1976): Über die wieder- holung gleichartiger Formen in der Entwicklungs- gesichte der Organismen, mit besonderer Berück- sichtigung der Congerien (Bivalvia).- Geol. vjesnik, 29, 75-89. PAPP, A. (1953): Die Molluskenfauna des Pannon im Wiener Becken.- Mitt. Geol. Ges., 44, 85-222, Wien. PAPP, A. (1954): Die Molluskenfauna im Sarmat des Wiener Beckens.- Mitt. Geol. Ges., 45, 63-68, Wien. SOKA», A. (1972): Pannonian and Pontian ostracod fauna of Mt. Medvednica.- Palaeont. Jugosl., 11, 1- 140, Zagreb. SREMAC, J. (1981): Some new and less known species of molluscs of the Croatica -beds and Banatica-beds in Northern Croatia.- Geol. vjesnik, 33, 107-121. VRSALJKO, D. (1997): Pannonian stratigraphy in the southwestern part of the Medvednica Mt.- Unpub- lished M.Sc. Thesis, University of Zagreb, 80 p. Manuscript received September 20, 1999. Revised manuscript accepted November 12, 1999.